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Questions and Answers
What is the main function of carbohydrates in living organisms?
How are carbohydrates classified based on the number of carbon atoms?
Which organic molecules are the most abundant in nature?
What is the storage form of energy in animals?
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Why are carbohydrates important in cell communication?
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What is the defining characteristic of isomers?
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Which of the following is an example of an isomer of glucose (C6H12O6)?
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What is the distinguishing feature between alpha and beta isomers?
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Which of the following statements about enantiomers is correct?
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What is the characteristic that distinguishes D-isomers from L-isomers?
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What type of bond links monosaccharides together to form disaccharides, oligosaccharides, and polysaccharides?
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Which of the following is not a type of disaccharide mentioned in the text?
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What type of bond is formed when carbohydrates are attached to non-carbohydrates?
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Which of the following is not a type of glycoside mentioned in the text?
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What type of bond connects the polysaccharide to the protein backbone in mucin?
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What is the purpose of digestion according to the text?
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Which enzyme is responsible for initiating carbohydrate digestion in the mouth?
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Which of the following is NOT a final product of carbohydrate digestion?
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Which cells are responsible for absorbing the monosaccharides produced during carbohydrate digestion?
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Which of the following dietary polysaccharides can be digested by most mammals?
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Where does the final digestion and absorption of carbohydrates primarily occur?
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Which organisms have the necessary enzymes to digest cellulose?
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Which transporter is responsible for the absorption of monosaccharides in the small intestine?
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Which of the following is NOT a major dietary polysaccharide?
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What is the primary cause of the symptoms associated with abnormal degradation of disaccharides?
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Which enzyme is responsible for the digestion of lactose?
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Which of the following is NOT a potential reason for abnormal degradation of disaccharides?
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What is the name of the product formed when monosaccharides are joined together?
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Which of the following is NOT a common monosaccharide found in nature?
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Where do the monosaccharides produced during carbohydrate digestion get absorbed?
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Which of the following is NOT a type of polysaccharide?
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What is the main function of glucosamine in the body?
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Which enzyme is responsible for the digestion of starch into maltose?
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What is the primary role of digestion in relation to nutrients?
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What is a characteristic of glucosamine in the context of carbohydrates?
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What is the primary purpose of the absorption process in relation to nutrients?
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Which of the following is a branched polysaccharide?
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What is the distinguishing characteristic of monosaccharides?
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Which of the following statements about the digestion and absorption processes is true?
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Which of the following is NOT a final product of carbohydrate digestion?
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Which process helps break down carbohydrates before digestion?
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Which of the following statements about the digestion of carbohydrates is correct?
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Which of the following is a major dietary polysaccharide?
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Which enzyme is responsible for the digestion of lactose, a disaccharide?
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Which of the following is a monosaccharide?
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Study Notes
Carbohydrates
- Carbohydrates (CH2O)n are the most abundant organic molecules in nature, serving as the main energy source for most animals, storage form of energy (in animals = glycogen), cell membrane components (glycoproteins – cell communication), and structural components (cell walls of plants, bacteria, fungi, algae; exoskeleton of insects).
Carbohydrate Classification
- Carbohydrates can be classified based on the number of carbon atoms (C).
- They can also be classified depending on the type of carbonyl group they contain (Aldo- or Keto-).
Carbohydrate Isomers
- Isomers have the same chemical formula but differ in structure or spatial arrangement of atoms.
- Examples of isomers include fructose, glucose, mannose, and galactose (C6H12O6).
- Alpha- and beta-isomers differ in the position of the carbon that carries the aldehyde/keto group.
Carbohydrate Enantiomers
- Enantiomers are special types of isomers that are mirror images of each other.
- Enantiomers are assigned as D- or L-sugars, with most sugars found in nature being D-isomers.
- D-isomers have the –OH group on the asymmetric carbon farthest from the carbonyl group (CHO) on the right, while in L-isomers, it is on the left.
- Most enzymes responsible for carbohydrate degradation are specific for either D- or L-isomers.
- Isomerases are enzymes capable of interconverting D- and L-isomers.
Monosaccharide Joining
- Monosaccharides can be joined to form disaccharides, oligosaccharides, and polysaccharides.
- The bonds that link sugars are glycosidic bonds.
- Disaccharides are formed by 2 monosaccharides, oligosaccharides by 3-10 monosaccharides, and polysaccharides by more than 10 monosaccharides (up to hundreds!).
- Important disaccharides include LACTOSE (galactose + glucose), SUCROSE (glucose + fructose), and MALTOSE (glucose + glucose).
- Important polysaccharides include Branched Glycogen (animal), Starch (plant amylose, amylopectin), and Cellulose.
Carbohydrates Linked to Non-Carbohydrates
- Carbohydrates can be attached to non-carbohydrates via glycosidic bonds, forming glycosides.
- Examples of glycosides include carbohydrates linked to:
- Purine and pyrimidine → Nucleic bases
- Aromatic rings → Bilirubin and steroids
- Proteins → Glycoproteins/proteoglycans
- Lipids → Glycolipids
- Mucin is a glycoprotein with an O-glycosidic bond between a polysaccharide and a protein backbone.
Digestion and Absorption
- Digestion is the process of breaking down complex nutrients into simple molecules.
- Absorption is the process of transporting these simple molecules across the intestinal epithelium.
- Absorption cannot occur if food is not digested, and digestion is fruitless if the digested nutrients cannot be absorbed.
Dietary Carbohydrate Digestion
- In most omnivores, carbohydrate digestion begins in the mouth with the enzyme salivary alpha-amylase (ptyalin).
- Carbohydrate digestion happens mainly in the small intestine, where pancreatic and enterocyte hydrolases (glycosidases) break glycosidic bonds.
- The final products of carbohydrate digestion are monosaccharides: glucose, fructose, and galactose.
- Monosaccharides are then absorbed by enterocytes (epithelial cells lining the inner surface of the small and large intestines).
Main Dietary Polysaccharides
- Main dietary polysaccharides include starch (plant) and glycogen (animal).
- Mastication helps break down material, but mammals generally do not have the enzymes necessary to break down cellulose β (1→4) glycosidic bonds.
- Ruminants and other herbivores have bacteria in their digestive tracts that produce enzymes to digest cellulose.
Final Digestive Processes and Absorption
- Final digestive processes and absorption occur at the mucosal lining in the duodenum and upper jejunum.
- Absorption of the monosaccharide products of carbohydrate digestion occurs by enterocytes.
- GLUT is a glucose transporter, and SGLT-1 is a sodium (Na+)-dependent glucose cotransporter.
Major Dietary Carbohydrates
- Major dietary carbohydrates include starch, glycogen, sucrose (saccharose), and lactose.
- Salivary amylase starts digestion, and further digestion is achieved by pancreatic enzymes in the lumen of the small intestine.
- Digestion is finished by enzymes synthesized by the intestinal mucosa, including maltase, isomaltase, lactase, and sucrase.
- Absorption of carbohydrates (monosaccharides) takes place in the duodenum and upper jejunum by Na+-dependent transport mechanisms (SGLT1) and facilitated transport (GLUT5 and GLUT2).
Abnormal Degradation of Disaccharides
- Abnormal degradation of disaccharides can lead to passage of disaccharides into the large intestine, increasing osmotic activity, and bacterial fermentation, resulting in abdominal cramps, diarrhea, and flatulence.
- Reasons for abnormal degradation include genetic defects, intestinal diseases, malnutrition, pharmaceuticals/drugs that injure the mucosa, lactose intolerance, and age-related reductions in enzyme activities.
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Description
Explore the functions and classification of carbohydrates, the most abundant organic molecules in nature. Learn about how carbohydrates serve as the main energy source for animals, storage form of energy, cell membrane components, and structural components in various organisms.
